Abstract:

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Gradient-dependent plasticity where a characteristic length is involved to consider the
microstructural effect (interactions and interplaying among microstructures due to the heterogeneous
texture) is introduced into Zerilli-Armstrong model based on the framework of thermally activated
dislocation motion. Effect of initial temperature on the distributions of plastic shear strain and
deformation in adiabatic shear band (ASB), the axial compressive stress-axial compressive strain
curve, the shear stress-average plastic shear strain in ASB curve and the plastic shear strain
corresponding to the occurrence of shear strain localization is investigated. The axial deformation
within aluminum-lithium alloy specimen in uniaxial compression in strain-hardening stage is
considered to be uniform. Beyond the peak compressive stress, a single ASB with a certain thickness
determined by internal length is formed and intersects the specimen. The axial plastic deformation is
decomposed into uniform deformation and localized deformation due to the shear slip along ASB.
Lower temperature leads to earlier occurrence of shear strain localization, i.e., lower critical plastic
compressive strain, steeper post-peak shear stress-average plastic shear strain in ASB curve, higher
peak shear stress and more apparent shear strain localization. The calculated distributions of plastic
shear strain and deformation in ASB are highly nonuniform due to the microstructural effect, as
cannot be predicted by classical elastoplastic theory applicable to completely homogenous material.
The predicted average plastic shear strains in ASB for different widths of ASB agree with the
measured values for under-aged Al-Li alloy at 298K and at strain rate of approximately 103s-1.

Abstract: Superplastic forming provides a good way for Ti alloys which are usually difficult to
be deformed. Ti75 alloy with a nominal composition of Ti-3Al-2Mo-2Zr is a newly developed corrosion resistant alloy, with a middle strength and high toughness. In the present paper, superplastic behavior of the alloy was investigated, the microstructural evolution in superplastic deformation was observed and the superplastic deformation mechanisms were analyzed. The results showed that the strain rate sensitivity, m, of the Ti75 alloy was larger than 0.3 and the strain was over 2.0 without surface cracking at 800°C and 5×10-4s-1 in compressive testing.
During the first stage of superplastic deformation, a phase grains became equiaxed, fine and homogeneous due to the recrystallization in a phase and diffusion in b phase. Newly formed equiaxed a grains then could slide and rotate, exhibiting superplastic features. The stress concentration caused by grain sliding of a grains could be released by slip and diffusion in b phase between the a phase grains, which acted as accommodation mechanisms.

Abstract: The hot deformation behaviors and microstructure in Al-Cu-Li alloy containing small
amount of Ag and Mg were investigated by transmission electron microscopy and isothermal
compression tests.When the strain rate is 0.1, 0.01 and 0.001s-1(the deformation temperature within
the range of 360-520􀀀 ) and 1 s-1(deformation temperature 520 􀀀 )respectively, the flow stress
decreases after a peak value, showing dynamic recrystallization,while the steady-state flow
characteristics exist on the other deformation conditions. The flow stress of Al-Cu-Li-Mg-Ag alloy
during hot deformation can be expressed by a Zener-Hollomon parameter in the hyperbolic-sine
function with the hot deformation activation energyDH of 250.45kJ/mol. The dislocations may
climb with support from many vacancies generated during hot deformation, thus forming lots of
helical dislocations. The dynamic precipitation and successive dynamic particles coarsening during
hot compression have been assumed to be responsible for further flow softening when deformed at
low strain rates.

Abstract: Uni-axial tensile plastic deformation behavior of rolled magnesium alloy AZ31B under the temperature range from room temperature(RT) to 250°C with strain rates between 10-3 and 10-1s-1 has been systematically investigated. Microstructure evolution and texture were determined using optical microscopy (OM) and electron back-scattered diffraction (EBSD) techniques, respectively. Our results indicated that the strength and elongation-to-fracture were more sensitive to strain rates at elevated temperature rather than that at room temperature; dynamic recrystallization (DRX) and relaxation of stress at elevated temperature resulted in dramatic change of mechanical properties. Compared with strain rate, the temperature played a more important role in ductility of AZ31B Mg alloy sheet.

Abstract: Anisotropic behavior at high temperature of an Aluminum-Lithium alloy was studied. Mechanical tests at a temperature of 350°C and a strain rate of 10-2 s-1 were carried out on samples taken at different angles with respect to the rolling direction of the sheet. Two plasticity criteria (HILL48 and HU2005) were identified and implemented in ABAQUS to predict the anisotropic behavior of the alloy for other angles. Results show that: (i) the alloy exhibits an anisotropic behavior at high temperature and some recrystallization occurs during plastic deformation; (ii) the coefficients of anisotropy depend on strain level and (iii) HU2005 criterion allows describing the behavior of the alloy at high temperature.